how to change the value of various custom properties at the same time?
Have a look at the operator simple template in the text editor. Replace main(context) with this

def main(context):
    #active pose bone
    pb = context.active_pose_bone
    # all custom properties on bone
    for key in pb.keys():
        #ignore _RNA_UI
        if key == '_RNA_UI':
            continue
        pb[key] = 1
        # insert a keyframe
        pb.keyframe_insert('["%s"]' % key)


and the poll method to

def poll(cls, context):
    return context.active_pose_bone is not None


to  make sure that there is an active pose bone selected.

and change the idname from  object.simple_operator to something meaningful like posebone.set

Then have a look at the panel simple template and 

row.operator("posebone.set")


will give you a UI button.